Single sideband quadricorrelator

A method for processing in-phase and quadrature signals from a quadrature hybrid of the form sin(.omega..sub.i -.omega..sub.o)t and cos(.omega..sub.i -.omega..sub.o)t to derive an output which represents the difference between the respective frequencies (.omega..sub.i -.omega..sub.o) where .omega..sub.i is the center frequency of the suppressed-carrier input signal m(t)sin .omega..sub.i t and .omega..sub.o is the center frequency of a locally generated reference oscillator, including the steps of:

• (1) differentiating the in-phase and quadrature signals;
• (2) multiplying the differentiated in-phase signal by the quadrature signal to obtain a first product;
• (3) phase shifting the in-phase signal 180.degree.;
• (4) multiplying the phase shifted in-phase signal by the derivative of the quadrature signal to obtain a second product;
• and
• (5) summing the first and second products to obtain the frequency difference output.

A bi-phase demodulator for acquiring and tracking the center frequency .omega..sub.i of the spread spectrum suppressed-carrier bi-phase modulated phase shift keyed input signal including:

• quadrature means for receiving a down converted signal of the form m(t)sin .omega..sub.i t and providing first and second signals of the form sin(.omega..sub.i -.omega..sub.o)t and cos(.omega..sub.i -.omega..sub.o)t, respectively;
• differentiator means for differentiating the first and second signals respectively;
• phase shift means for phase shifting the first signal 180.degree.;
• first and second multiplier means for multiplying the differentiated first signal by the second signal and for multiplying the phase shifted first signal by the differentiated second signal, respectively;
• first summing means for summing the outputs of the first and second multipliers to provide a frequency difference term (.omega..sub.i -.omega..sub.o);
• second summing means for coupling the output of the first summing means to a voltage controlled reference oscillator;
• first and second matched low pass filters for filtering said first and second signals;
• third multiplier means for multiplying said filtered first and second signals;
• and
• loop filter means for deriving from said third multiplier means a DC error voltage for controlling said voltage controlled reference oscillator via said second summing means whereby the output of said voltage control oscillator accurately tracks the suppressed-carrier of the input signal via the quadrature hybrid.